The present state of art for production of synthetic fuels from either coal or natural gas (the two major possible raw materials) involves initial production of synthesis gas which is then either converted directly to hydrocarbons (Fischer-Tropsch) or converted first to methyl alcohol, which subsequently is converted into hydrocarbons (Mobil process): ##STR1##
The Fischer-Tropsch process, although proven commercially, is not the most economically desirable process for the future due to its two very energetic steps and unsuitable product composition. The Mobil process is capable of producing gasoline-range hydrocarbons and aromatics relatively free of heavies, but suffers from the disadvantageous economics of first producing synthesis gas, which is then converted into methyl alcohol, which in turn is converted into hydrocarbons.
My discovery follows an independent and new route by utilizing methane (or natural gas) as the basic raw material. Methane as natural gas or even biological "deep methane" is expected to be available well into the 2000's, and, if not utilized exclusively as an energy source but rather for transportation fuels and as a chemical raw material source, could last much longer. Furthermore, coal can be readily converted into methane by methanation or by in-situ gasification, thus avoiding difficulties in mining and transporting coal. Further, alternate sources of methane, such as the biological conversion of biomass (sewage recycling, utilization of plant life on land and sea [algae or kelp farming of the sea] with subsequent off shore conversion allowing the piping of methane to land), are becoming available. If in the future cheaper atomic or fusion energy becomes available, during off-peak periods, these plants could become producers of aluminum carbide which, upon hydrolysis, gives methane (with ethane and ethylene as by-products.) The conversion of methane to higher hydrocarbons thus represents a viable new alternative to synthetic hydrocarbon processes.
The oligocondensation of methane was discovered by Olah et al., Journal of the American Chemical Society, 90, 2726 (1968), using exceedingly strong acid systems, the so-called "superacids" comprising a mixture of fluorosulfuric acid and antimony pentafluoride ("magic acid"), a mixture of hydrogen fluoride and antimony pentafluoride, or related superacids. Superacids have a Hammett acidity function H.sub.o less than -11.9H.sub.o, the value for 100 percent sulfuric acid. However, yields were extremely low and the superacid was reductively depleted, rendering the process impractical on a commercial scale.
Alkane-alkene condensations (alkylations) such as that of isobutane with isobutylene to produce C.sub.8 alkylate is well known in the petrochemical industry. Olah reported first the alkylation of alkanes with alkyl cations, generated in superacidic media [J.Am.Chem.Soc., 96, 4939-4952 (1973)].
The condensation (polymerization) of methane and olefins represents a special problem and for a long time, methane was considered to be inert to usual acid catalyzed electrophilic reactions. The work of Olah on the superacid catalyzed reactivity of methanes opened up the possibility for such reactions. D. T. Roberts, Jr. and L. E. Calihan [J.Macronol.Sci-Chem., A7 (8) pp. 1641-1646 (1973)] reported that mixtures of methane and olefins (ethylene, propylene, etc.) polymerized in an autoclave at room temperature over a liquid magic acid (HSO.sub.3 F/SbF.sub.5) catalyst to give oily oligomers with molecular weight of 100 to 700. Conversions were low (in the case of methane and ethylene, 5%) and under the used liquid phase conditions with long contact times (generally 24 hours) the olefin itself tended to polymerize on its own. Subsequently using another liquid superacid catalyst, hydrogen fluoride-tantalum pentafluoride, Siskin carried out the alkylation of methane with ethylene in a pressurized flow system [J.Am.Chem. Soc., 98, 5413 (1976)]. No yields or conversions were given and again the liquid phase reaction conditions were considered to substantially limit practical application of the reaction.